The present invention relates to an installation for calcining a mineral load containing a carbonate in order to produce a hydraulic binder, of the type comprising at least one calciner, the installation successively comprising a preheater, at least one calciner for producing a hydraulic binder comprising a combustion chamber and a cooler; the combustion chamber having:                means for introducing the mineral load into the chamber, connected to the preheater;        combustion means for maintaining the chamber at a temperature between 700° C. and 900° C., the combustion means having means for introducing an oxidizing gas for combustion coming from the cooler into the chamber;        additional means for introducing a treatment gas having a controlled carbon dioxide content into the chamber in order to oppose the dissociation of the carbonate in the chamber; and        means for removing the calcined mineral load that open into the cooler;the installation comprising means for discharging the flue gases coming from the or each calciner into the atmosphere.        
The term “hydraulic binder” is understood to mean a powdery material composed of fine particles, which, in contact with water, react by forming a solidified block and develop mechanical strength properties. Examples of hydraulic binders are cements, limes, slags, pozzolans and ash from fossil fuel power stations.
The aforementioned installation is intended to produce an artificial hydraulic binder denoted by the term “kalsin”, as described in application EP-A-0 167 465.
Kalsin-type binders are products based on clay phases and on at least one carbonate, preferably a calcium carbonate with optionally a magnesium carbonate. The carbonate is activated by dehydroxylation and by calcium compounds, without forming free lime.
The term “carbonate” denotes a salt resulting from the combination of carbonic acid with a base. This salt comprises a carbonate anion and a metal cation, preferably an alkali or alkaline-earth metal cation.
The installation may also produce, at the same time as the kalsin, cement clinker. The term “cement clinker” is understood to mean the material exiting a fuel-fired rotary kiln, said material having formed balls or granules by partial melting at high temperature, for example around 1500° C., and by chemical compounds of various oxides such as calcium, silicon, aluminum and iron oxides. The clinker thus obtained is, after grinding with suitable additives, capable of producing a cement. A known installation for producing clinker is described in EP 0 754 924.
Known from the article “High energy savings through the use of a new high performance hydraulic component” by M. Paliard and M. Makris, in the work “Energy efficiency in the cement industry” edited by J. Sirchis, from Elsevier publishers (1990) is an installation for producing kalsin of the aforementioned type, which comprises a calciner having a fuel combustion region, into which an oxidizing gas for combustion that comes from the cooler is introduced, and a region for containing the load to be calcined, into which a gas having a controlled carbon dioxide partial pressure is introduced.
The carbon dioxide partial pressure is high in the containment region in order to oppose the dissociation of the carbonates.
However, the carbon dioxide that is introduced into the containment region is expelled into the atmosphere, which contributes to increasing the pollutant emissions in the atmosphere.